During the War of 1812, Beaumont enlisted in the army as a medical officer. In 1822, while serving a military physician at Fort Mackinac, MI, he spent three years caring for a patient that was shot in the stomach and left with a permanent hole. As a result, he was able to perform the first comprehensive studies on the digestive system. In 1833 he published a book entitled, Experiments and Observations on the Gastric Juice and the Physiology of Digestion, which detailed his study of the digestive system on his military patient.

In 1834, Doctor Beaumont was sent to Jefferson Barracks to take over as surgeon and medical officer. In 1836, he was appointed chairman of surgery for the new medical at Saint Louis University. He became a prominent St. Louisian, socializing with William Clark, William Greenleaf Eliot, and Robert E. Lee.

Beaumont resigned from the military due to deafness, and in 1846, he was appointed as a consulting physician to the new St. Louis City Hospital, where he treated many cholera patients. The street where his home was located was named Beaumont Street and Beaumont High School is named after him. [Final Resting Place, p. 31]